1. Field of Invention
The invention relates generally to printing products and more particularly to a method and apparatus for automatic trimming of printed products, such as brochures, magazines, catalogues, and book blocks.
2. Description of the Related Art
Conventional apparatuses for automatic trimming of printed products, such as brochures, magazines, catalogues, and book blocks, are provided with a trimming station including one or more blades positioned on a vertically moving yoke. The printed products are supplied successively from a feeding conveyor to the trimming station, where the printed products are trimmed on the edges by one or more blades.
One such conventional trimming apparatus, disclosed in document European Patent document EP 1 166 977 A1, is a so-called three-side trimmer, in which one blade of the trimming station trims the front edge of one printed product while two other blades simultaneously cut the top and bottom of another printed product. The printed products are supplied to the trimming station from a conveying belt that includes a number of dividers, against which the printed products are lined up. At the end of the conveying belt, the printed products are clamped and held in place between an upper and a lower belt before being supplied to a trimming transport device in the trimming station. In the trimming transport device, once the printed product has reached the predetermined position, the front edge of the product is trimmed by the first blade. The printed product is then transported further within the trimming transport device, where the top and bottom edges of the printed products are trimmed by the other two blades. In order to trim the desired position of the printed products, a mechanical stoppage device may be provided within the trimming transport device. However, in order to trim the desired position of the printed products more accurately, the trimming station may be provided with a measuring unit that controls the stoppage of the printed material before the trimming takes place. Using the measuring unit, it is possible to dispense with a mechanical stoppage device and hold the printed products in place between an upper belt and a lower belt within the trimming transport device for trimming. With a mechanical stoppage device, however, the printed products would have to be released before the desired stoppage point is reached.
It is often desirable to trim printed products with varying widths. For example, printed products intended for shipping, in particular by postal mail, may be produced with varying widths. This can be the result of the so-called “selective binding” on a gathering and wire-stitching apparatus. With digital printing presses, these products can be produced successively and such that the format differs from one printed product to another.
The conventional trimming apparatus discussed above can be used to trim printed products having different widths. To do so, however, a coupling of the drive must be disengaged, the apparatus shut down, and the operation interrupted. Therefore, changing the format of one or more printed products is not practical and cost-effective. Accordingly, it is advantageous to provide a trimming apparatus and a trimming method, which permit the trimming of successive printed products having varying widths at full operational speed without reducing output.